This invention relates to standards for lights and more particularly to breakaway assemblies for light standards.
Breakaway assemblies are used for the support of standards for lights, signs, parking meters and the like. Such breakaway assemblies are designed to readily fail when the supported structure is subjected to lateral impact such as may be applied by a colliding automobile. At the same time, the breakaway assembly must have sufficient tensile and compressive strength to withstand wind loads which are applied to the supported structure by the application of winds prevalent in a particular geographic area. Supported structures desirably must fail under impact force so as to substantially reduce the severity or eliminate injury to motorists who collide with a supported structure 10 during an accident. The breakaway assembly is designed to give way upon impact of the automobile so as not to apply a substantial deceleration force to the automobile and thus the driver or passengers.
In 1985, AASHTO formulated new regulations for breakaway standards to be installed on federal highways. These regulations, more particularly set out in Section 7 thereof, require that the pole structures give way when struck with less impacting mass than that previously required. This lower impacting mass requirement has been caused by the construction of lighter cars. These new regulations become effective July 1, 1990.
There are three common types of breakaway assembles for standards. The slip base type includes two flanges gripped together such that when the standard is struck, the slip base or pole flange slides away from the base or base flange affixed to anchor bolts imbedded in the foundation for the standard. U.S. Pat. No. 4,007,564 discloses a breakaway coupling device employing a fracture mode of crack propagation; i.e., the coupling(s) rupture or split upon impact, releasing the pole to move away from the foundation. Another type of breakaway assembly is the transformer base. The transformer base type mounts the standard on a housing approximately 15" to 24" high. The housing is a cast box and is frangible. Upon impact, the frangible housing fractures and splinters. One advantage of this type of housing is that often the standard is not damaged and can be salvaged. The housing becomes a sacrificial assembly.
Although the manufacturers of the prior art breakaway assemblies are attempting to redesign the prior art assemblies to meet the new specifications. This task is more difficult due to higher stress requirements due to taller poles, yet must fracture or release under lower impact mass. For example, in the use of the slip base, the standard may bend and place the slip bolts in tension preventing the slip base from slipping off the base flange. To design a transformer base which is sufficiently frangible to meet the new specifications, the new design may have less ability to withstand wind loads, particularly in the range of 80 to 100 mph winds. This is particularly a problem in certain geographic areas where the wind loads are high and require sturdier standards. The coupling with a flanged base mounted on top is more expensive when compared to the present invention herein described.